1. Field of the Invention
The invention relates generally to audio amplification systems, and more particularly to systems and methods for detecting the impedance of an output load coupled to a digital amplifier and compensating for changes in the frequency response of the amplifier.
2. Related Art
Pulse Width Modulation (POMPWM) or Class D signal amplification technology has existed for a number of years. POM PWM technology has become more popular with the proliferation of Switched Mode Power Supplies (SUMPSSMPS). Since this technology emerged, there has been an increased interest in applying POM PWM techniques in signal amplification applications as a result of the significant efficiency improvement that can be realized through the use of Class D power output topology instead of the legacy (linear Class TAB) power output topology.
Early attempts to develop signal amplification applications utilized the same approach to amplification that was being used in the early SUMPS SMPS. More particularly, these attempts utilized analog modulation schemes that resulted in low performance applications. These applications were complex and costly to implement. Consequently, these solutions were not widely accepted. Prior art analog implementations of Class D technology have therefore been unable to displace legacy Class TAB amplifiers in mainstream amplifier applications.
Recently, digital POM PWM modulation schemes have surfaced. These schemes use Sigma-Delta modulation techniques to generate the POM PWM signals used in the newer digital Class D implementations. These digital POM PWM schemes, however, did little to offset the major barriers to integration of POM PWM modulators into the total amplifier solution. Class D technology has therefore continued to be unable to displace legacy Class TAB amplifiers in mainstream applications.
One of the problems with prior art systems and methods is that the quality and performance of the discrete output power switches and their associated drivers is unknown and varies as the performance and demand of the application change.
Another problem with prior art systems and methods is that the performance and quality characteristics of the remainder of the signal processing system vary with the applications in which they are used. Because the exact implementation in each system and the end-user applications are not deterministic, each system requires a point solution. These point solutions are not flexible, scaleable or transportable across applications.
Yet another problem with prior art systems and methods is that their frequency responses vary with changes in the respective load impedances. In a conventional open loop system, an output reconstruction filter produces a low-pass filter response that is dependent upon the output load. As the load of a particular system is increased, the high frequency response of the system decreases in a predictable manner.
Because of these problems with the prior art, it would be desirable to provide systems and methods to detect changes in output loads and to compensate for these changes to maintain an optimal frequency response and optimal performance.